A computer program such as a browser, for example, configures a computer to generate user interface information based at least in part upon code such as HTML, CSS and javascript downloaded from another computer such as a web server, for example. Defects and/or vulnerabilities in the downloaded code can be harmful to the operation of a computer configured to use such code, such as a computer configured to implement a browser, for example. Defects in a program running on a web server, for example, that produces the downloaded code can result in the defects or vulnerabilities in the downloaded code that put at risk a computer configured to use such code.